Hydraulic operating mechanism for a rotary chuck

ABSTRACT

A pressure control device for a swivel coupling with a cylinder in the turning coupling part and a piston therein forming a chuck-closing cylinder side, a conduit for hydraulic fluid and including a port in the coupling leading to this cylinder side and crossing the stationary and turning coupling parts, port sealing means in the coupling at the port crossing, and a check valve in the conduit normally closed to block fluid flow from the chuck-closing cylinder side, with the device featuring a bypass in the conduit around the check valve and having a constriction.

United States Patent 1 1 1111 3,922,952

Roddy et a1. 1 1 Dec. 2, 1975 [5 1 HYDRAULIC OPERATING MECHANISM3.364.823 H1968 Benjamin 91/420 FOR A ROTARY CHUCK 3,434.448 3/1969Woodfill 91/420 X 3,735,670 5/1973 Smithson 91/420 [75] Inventors: JohnJ. Roddy, Meriden; Alfred G.

Higley, E fi ld both of Con FOREIGN PATENTS OR APPLICATlONS 906,01391962 U t d K' d ..9131 [73] Ass1gnee: Cushman lndustr1es,lnc0rp0rated,m e mg Hartford, Conn.

Primary E.\'ammerlrw1n C. Cohen [22] Filed: Apr. 4, 1973 Attorney,Agent, or Firm-Walter Spruegel 1211 Appl. No.: 347,922 I 57 ABSTRACT 52us. c1. 91/29; 91/31; 91/420; A P Control device for swivel Coupling i11 137/110; 279/4 cylinder in the turning couplmg part and a piston 51Int. Cl. ..Fl5B 11/08; F158 13/042- therein forming a chuck-ClosingCylmder side, a

B23B 3H3O duit for hydraulic fluid and including a port in the [58]Field of Search 91/420, 29, 2s, 31; Coupling leading to this CylinderSide and o sing the 137/110; 279/4 stationary and turning couplingparts, port sealing means in the coupling at the port crossing. and a[56] References Cited check valve in the conduit normally closed toblock UNITED STATES PATENTS fluid flow from the chuck-closing cylinderside, with the device featuring a bypass in the conduit around 3,164,9591/1965 Gondek 91/420 the Check valve and having d constriction.

3,233,407 2/1966 Smith v. 91/420 X 3,248,931 5/1966 Berger, Jr. et aL.91/31 X 5 Claims, 4 Drawing Figures 3,349,671 10/1967 Hoffman 91/420HYDRAULIC OPERATING MECHANISM FOR A ROTARY CHUCK This invention relatesto fluid-operated chucks in general, and to hydraulic operatingmechanism for rotary chucks in particular.

Conventional hydraulic or pneumatic chuck operating mechanism provides acylinder, usually doubleacting, and a piston therein, as well as aswivel coupling. The cylinder is customarily adapted for mounting on thechuck-carrying spindle of a lathe or the like so as to be turnabletherewith, and the piston is adapted for operative connection with thejaw actuator of the chuck, while the swivel coupling has companion partsof which one part forms and, hence, turns with the cylinder, and theother part is connectible with two conduits and is held againstrotation, with these coupling parts being suitably ported for the flowof operating fluid between the conduits and the opposite sides,respectively, of the cylinder. There is also provided a usual controlvalve which is connected with the conduits, and is operable to admitoperating fluid under pressure from a suitable source to either thechuckclosing or chuck-opening cylinder side and simultaneously vent theother cylinder side.

The present invention is concerned with a type of chuck operatingmechanism which will act to lock the operating fluid in the chuckclosing cylinder side whenever the pressure of the fluid therein isabove the pressure of the supply fluid. This is achieved by interposinga check valve in a part of the fluid passage which is close to and leadsto the chuck-closing cylinder side, with the check valve opening toadmit fluid into, but closing to block fluid flow from, this cylinderside, and providing a plunger which is subjected to fluid in the fluidpassage to the chuck-opening cylinder side, and which on admission ofoperating fluid into this passage for work release, opens the checkvalve for venting the chuck-closing cylinder side. In using a checkvalve in this fashion, the same will even close when the pressure of thefluid in the chuck-closing cylinder side is substantially equal to thatof the supply fluid. The advantage of this type of mechanism is thatonce work is gripped by the associated chuck and the pressure of thefluid supplying the chuck-closing cylinder side should thereafter dropsuddenly from any cause whatever, such as a sudden leak in the fluidpassage ahead of the check valve, for example, the chuck maynevertheless be driven and the work machined without giving rise torelaxation of the chucks grip on the work and the hazards this wouldinvolve.

While this type of chuck operating mechanism is entirely satisfactoryfor pneumatic operation, it has been found totally unsuitable forhydraulic operation, in that the very lock of the operating fluid in thechuck-closing cylinder side, which is to take place on the slightestsudden pressure drop of the supply fluid, will give rise to anuncontrollable and potentially quite hazardous pressure increase ofhydraulic fluid in this cylinder side at no pressure drop whatever ofthe hydraulic fluid ahead of the check valve. This is due to the factthat the imperative port seals in the swivel coupling between thestationary and turning parts thereof are subject to friction whichincreases with chuck operating speed, and which is even higher for theseal or seals that are associated with the port in the coupling leadingto the chuck-closing cylinder side and, hence, are constantly subjectedto the pressure load of the hydraulic fluid in chuck operation, and theensuing heat generated in the seals and coupling, while generallytolerable, does raise the pressure of the hydraulic fluid in thecoupling. While heat-up, and ensuing increase in pressure of thehydraulic fluid in the coupling from this friction cause is of noconsequence for the hydraulic fluid ahead of the check valve, it is ofthe gravest consequence for the hydraulic fluid in the chuck-closingcylinder side because this fluid will, under increasing pressure fromthis friction cause, soon close the check valve though the pressure ofthe supply fluid has not dropped at all, and once this check valve isclosed and the hydraulic fluid in the chuck-closing cylinder side thustrapped therein, this trapped hydraulic fluid will further be heatedwith ensuing further increase of its pressure that soon will reachintolerable and highly hazardous proportions.

It is the primary aim and object of the present invention to providechuck operating mechanism of this type which does lend itself tohydraulic operation.

It is another object of the present invention to provide chuck operatingmechanism of this type which embodies the described structure of, andfunctions as, the aforementioned prior chuck operating mechanism of thistype, but which does not give rise to any adverse pressure increase ofhydraulic operating fluid in the chuck-closing cylinder side, and forthat reason is to lend itself to highly desirable hydraulic operation.

It is a further object of the present invention to provide hydraulicchuck operating mechanism of this type which embodies the structure of,and functions as, the aforementioned prior mechanism of this type and,hence, includes a check valve, now referred to as main check valve, inthe fluid passage to the chuckclosing cylinder side, and in which anyappreciable pressure increase of hydraulic fluid in the chuckclosingcylinder side is prevented by a pressure control device which, onoperational closure of the main check valve in any started chuckoperation, functions to bleed from the chuck-closing cylinder sideenough hydraulic fluid to keep the pressure of the remaining fluidtherein at a level which is entirely safe, on the one hand for theduration, no matter how long, of the started chuck operation duringwhich the pressure of the supply fluid undergoes no sudden drop, and onthe other hand until after a sudden pressure drop of the supply fluidpreferred automatic controls responsive thereto have stopped the powerdrive of the chuck. In order to function in this manner, the pressurecontrol device may also be of exceeding structural simplicity byproviding in the fluid passage to the chuck-closing cylinder side abypass around the main check valve, and a constriction this bypass.

Another object of the present invention is to provide chuck operatingmechanism of this type in which the aforementioned pressure controldevice further functions to stop bleeding of excess hydraulic fluid fromthe chuck-closing cylinder side on a sudden pressure drop of thesupplying fluid ahead of the main check valve, to thereby keep worksafely gripped after sudden pressure drop for a time period during whichmany started chuck operations are finished, or if not finished willenable responsive automatic controls to bring the power drive of thechuck to a safe stop, without giving rise to any potentially hazardousincrease in pressure of the hydraulic fluid in the chuck-closingcylinder side. To this end, the pressure control device further providesin the bypass a secondary valve which, when open, forms part of thebypass, with the constriction being in a part of the bypass other thanthat between the secondary valve and the fluid passage behind the maincheck valve, i.e., the fluid passage from the latter to thechuck-closing cylinder side, and also provides an in- -strumentalitywhich is subjected to hydraulic fluid in the fluid passage ahead of andbehind the main check valve, and operative to open and close thesecondary valve when the pressure of hydraulic fluid in the fluidpassage behind the main check valve is within a certain range and isabove this range, respectively, with the range being from a pressure atleast equal to, to a pressure of predetermined excess over, the pressureof hydraulic fluid in the passage ahead of the main check valve.

A futher object of the present invention is to provide chuck operatingmechanism of this type, of which the aforementioned secondary valve inthe bypass of the pressure control device is in its preferred form asecondary check valve of inherent automatic operation which is normallyclosed to block fluid flow from the fluid passage behind the main checkvalve to the fluid passage ahead of the main check valve, and theinstrumentality of this control device preferably provides a slidablestepped plunger with larger and smaller ends exposed to hydraulic fluidin the fluid passage ahead and behind the main check valve,respectively, whereby this plunger is stepped into advance and retractpositions when the total pressure of fluid on the larger plunger endchanges from smaller to greater and from greater to smaller,respectively, than the total pressure of fluid on the smaller plungerend, and the plunger being arranged to act on its advance and retractsteps to open the secondary check valve and permit its closure,respectively.

It is a further object of the present invention to provide chuckoperating mechanism of this type, of which the bypass of the pressurecontrol device is formed, between the constriction and the secondarycheck valve therein, with a reservoir, and the entire smaller plungerend is exposed to and forms part of this reservoir. With thisarrangement, the constriction will on operational closure of the maincheck valve, on the one hand at no sudden pressure drop of the supplyfluid ahead of this valve, permit bleeding from the reservoir ofsufficient fluid to keep the fluid in the chuck-closing cylinder side atapproximately the pressure of the supply fluid despite any operationalheat-up of the fluid in this cylinder side, and on the other hand at asudden pressure drop of the supply fluid ahead of the main check valve,permit bleeding of fluid from the reservoir at such a very low rate thatthe prevailing pressure of the reservoir fluid immediately after suchsudden fluid pressure drop is entirely adequate forcefully to step theplunger to its retract position and, hence, permit closure of thesecondary check valve before the pressure of the fluid in thechuck-closing cylinder side undergoes any appreciable drop.

Further objects and advantages will appear to those skilled in the artfrom the following, considered in conjunction with the accompanyingdrawings.

In the accompanying drawings, in which certain modes of carrying out thepresent invention are shown for illustrative purposes:

FIG. 1 is a fragmentary longitudinal section through hydraulic chuckoperating mechanism embodying the invention;

FIG. 2 is a longitudinal section through hydraulic chuck operatingmechanism embodying the invention in a modified manner; and

FIGS. 3 and 4 are fragmentary diagrammatic sections through hydraulicchuck operating mechanisms embodying further modifications of theinvention.

Referring to the drawings. and more particularly to FIG. 1 thereof, thereference numeral 10 designates chuck operating mechanism which providesas its major operating components a swivel coupling 12 and a fluidpressure control device 14 which in this example is embodied in acontrol unit 16 separate from the swivel coupling 12.

The swivel coupling 12 comprises companion parts 18 and 20, of which thecoupling part 18 provides a cylinder 22 with a piston 24 thereindefining in the cylinder opposite sides 26 and 28. The coupling part 18is adapted for mounting on the power spindle of a lathe or the like(neither shown) and, hence, is operationally turning therewith, whilethe other coupling part 20 is held stationary and is mounted on theturning coupling part 18 through intermediation of an antifrictionbearing 30. The piston 24 is connected with a drawbar 32 which in turnis adapted for connection with a jaw actuator in a chuck carried on thepower spindle of the lathe. In the present example, the jaws of thechuck are closed on work when fluid under pressure is admitted to thechuck-closing cylinder side 26 and the other chuck-opening cylinder side2 is vented, and the jaws of the chuck are open when fluid underpressure is admitted to the chuck-opening cylinder side 28 and thechuck-closing cylinder side 26 is vented.

To pass fluid to and from the cylinder sides 26 and 28, the coupling 12is provided with passages 34 and 36 which lead from openings 38 and 40in the stationary coupling art 20 across the coupling parts 20, 18 tothe chuck-closing and chuck-opening cylinder sides 26 and 28,respectively. To seal the fluid passages 34 and 36 at their crossingsfrom one coupling part to the other coupling part, there are providedsuitable seals which are subjected to operational friction owing to thefact that one coupling part is stationary and the other coupling part isoperationally turning. In the present instance, there are providedcompanion seals 42 and 44 which are carried by the stationary andturning coupling parts 20 and 18, respectively. The seal 42 provides inthis instance outer and inner rings 46 and 48 in outer and inner bearingrings 50 and 52 which are slidable on the outer and inner peripheralwalls 54 and 56 of a ring-shaped recess 58 in the stationary couplingpart 20. The other seal 44 is in the form of a ring 60 on the turningcoupling part 18, with this ring 60 having a ring-shaped recess 62. Theouter and inner rings 46, 48 of the seal 42 and their bearing rings 50,52 are spaced by an annular gap g which leads from the recess 58 in thestationary coupling part 20 to the recess 62 in the other seal 44, withthe recess 58, gap g and recess 62 forming part of the fluid passage 36to the chuckopening cylinder side 28. The outer and inner rings 46, 48of the seal 42 are by springs 64 urged into sealing engagement with thering seal 44.

The control unit 16 provides a casing which in this instance is fixedlymounted separately from the coupling 12. The casing 70-is provided withan inlet 72, an outlet 74 and a port 76 connecting them, and is furtherprovided with another inlet 78, another outlet 80 and a port 82connecting the latter with the inlet 78. The

leads to the outlet 80. The outlets 74 and 80 are connected, in thisinstance by conduits 110 and 112, with the opening 38 and 40,respectively, in the stationary coupling part 20, wherefore the ports 76and 82, are through the conduits 1 and 112 and fluid passages 34 and 36in the coupling 12, in communication with the chuck-closing andchuck-opening cylinder sides 26 and 28, respectively.

The fluid pressure control device 14 includes the ports 76 and 82 in thecasing 70, and provides various control elements which in this instanceare arranged in the casing 70. Among these control elements is a maincheck valve 114 which is interposed in the port 7 6 and in this instancemounted in the annular recess 90,with

if not then closed, will immediately close and thus traip in thechuck-closing cylinder end the fluid therein which will be at anentirely safe operating pressure for the remainder of the started chuckoperation. After the chuck operation is then concluded, the mentionedcontrol valve is actuated to admit fluid under pressure to the inlet 78and, hence, to the chuck-opening cylinder side 28, and simultaneouslyvent the inlet 72. The moment theadmitted fluid under pressure reachesthe port 82 in the casing 70, and more particularly the side 100 of thecylinder chamber 88, the fluid therein will shift the piston 116 to theleft into a position in which its pin 118 opens the check valve 114 forventing the chuck-closing cylinder side 26.

Safe conclusion, by virtue of the check valve 114, of any started chuckoperation on any sudden pressure drop of the supply fluid, is certainwhen the mechanism is operated pneumatically and the operating fluid isair as usual. However, the present mechanism as described this checkvalve 114 being normally closed to block fluid flow from the outlet 74,and hence from the chuck-closing cylinder side 26, to the inlet 72, andthis check valve dividing the port 76 into sections 76 and 76", of whichthe port section 76" is open to the chuck-closing cylinder side 26 andthe port section 76 is open to the inlet 72. Associated with thechec-kvalve 114 is a piston 116 in the cylinder chamber 88, with thispiston having a pin 1 18 for opening the check valve 114. The inlets 72and 78 are, through conduits, connected with a usual control valve (notshown) which is operative to admit fluid under pressure from asuitablesource to either inlet 72 or 78 and simultaneously vent the other inlet.

In operation of the mechanism 10, and assuming that work is to begripped by an associated chuck and to be machined in the power-drivenchuck, the mentioned control valve is operated to admit fluid underpressure to the inlet 72 and simultaneously vent the other inlet 78 and,hence, also the chuck-opening cylinder side 28, with the admitted fluidunder pressure opening the normally-closed check valve 1 14 and passingto the chuckclosing cylinder side 26 to cause the chuck to grip thework. The power drive of the chuck-carrying power spindle is nextstarted, whereupon the gripped work is machined. Once fluid underpressure from the source is admitted to the inlet 72 and passed to thechuckclosing cylinder side 26, the pressure of the fluid in the latterwill quickly equal that of the source so that the check valve 114 willthen close and remain closed as long as the pressure of the fluid inthis cylinder side remains substantially equal to that of the source.However, if for any reason the pressure of the fluid in this cylinderside should be below that of thesource, the check valve 114 will beopened until substantial fluid pressure equilibrium is established. Thefluid pressure source, in the case of hydraulic operating fluid atleast, is usually the output of a pump of preferred regulatable outputpressure. The primary purpose of the check valve 114 is, of course, torender a chuck operation safe in the event that in the course of thelatter the pressure of the supply fluid should suddenly drop from anycause, such as pump failure or a sudden leak in the fluid line from thepump to the check valve 114. In the event of such a sudden pressuredrop, the check valve 114,

so far, and including the check valve 1 14, does not lend itself to safechu'ck operation at any time if the mechanism is operated hydraulically,with oil being then the usual operating fluid. This is due to the factthat when the chuck, and hence also the turning coupling part 18, arepower-driven, the seals 42 and 44 undergo operational friction, wherebythere is generated in these seals heat which is transmitted to thecoupling 12 and, hence also to the operating fluid in the chuck-closingcylinder side 26, with this operating fluid, when hydraulic and, hence,non-compressible, undergoing increasing pressure with increasing heat.Thus, with operational heatup, from this friction cause, of thehydraulic fluid in the chuck-closing cylinder side 26 and back to thecheck valve 114 being progressive in the course of a chuck operation,its correspondingly progressively increasing pressure will soon closethe check valve 114, if the same is not already closed, even at nopressure drop whatever of the hydraulic supply fluid in the line up tothis check valve. Progressive increase in pressure of the hydraulicfluid thus trapped in the chuck-closing cylinder side in the course of achuck operation is thus inevitable and the pressure of this trappedhydraulic fluid will soon reach hazardous proportions before manystarted chuck operations would be concluded.

In accordance with the invention, provisions are made whereby. chuckoperation is rendered entirely safe when the operating fluid for themechanism 10 is hydraulic fluid. To this end there is provided in thefluid passage from the pressure source to the chuckclosing cylinder sidea bypass 120 around the check valve 114, with this bypass having aconstriction 122. In the exemplary chuck operating mechanism 10, thebypass 120 with the constriction 122 is provided in the port 76 -in thecasing around the check valve 114 therein, and the bypass is formed inthis instance by an orifice 124, a chamber 126, an orifice 128, the

constriction 122, a chamber 130, an annular recess draulic fluid underthe source pressure has just been admitted to the chuck-closing cylinderside 26, the check valve 114 will close when substantial pressureequilibrium prevails in the port sections 76' and 76" on opposite sidesof the check valve 114. On then starting the power drive of the chuck,the pressure of the hydraulic fluid in the chuck-closing cylinder side26 will,

during closure of the check valve 114, soon start to increase due toheat-up emanating from inevitable heatup of the seals 42 and 44 fromoperational friction, with any pressure increase of the hydraulic fluidfrom this cause spreading throughout the trapped fluid from the checkvalve 114 to and including the chuck-closing cylinder side. However,even the slightest increase in pressure of this trapped hydraulic fluidwill force or bleed from the latter through the constriction 122sufficient fluid to keep the pressure of the trapped fluid substantiallyat the normally constant pressure of the supply fluid in the portsection 76 for any duration of a chuck operation and regardless of theextent of operational heat-up of the trapped fluid. The chuck operatingmechanism is thus entirely safe for any and all chuck operations, exceptin the event that the supply pressure of the hydraulic fluid shouldsuddenly drop from any cause whatever, such as pump failure or a suddenleak in the fluid supply line from the pump to the check valve 114.However, the chuck operating mechanism 10 is, nevertheless easilyrendered safe for any and all chuck operations by providing knownautomatic control which senses the pressure of the hydraulic supplyfluid, as that in the port section 76' for example, and which ispresettable to a still safe work-gripping pressure below normaloperating pressure, and operates when the sensed pressure is equal tothe preset pressure to stop the power drive of the chuck. Thus, even inthe event of a sudden pressure drop of the hydraulic supply fluid duringa chuck operation, the work will remain safely gripped until the chuckcomes to a safe stop very soon after this control goes into action.

In accordance with a further aspect of the invention, further provisionsare made to stop bleeding through the constriction 122 of hydraulicfluid from the trapped fluid between the chuck-closing cylinder side 26and the check valve 114 on a sudden pressure drop of the hydraulicsupply fluid. To this end there is provided an instrumentality 138, andthere is, in the part of the bypass 120 between the constriction 122 andthe port section 76", a valve 140 which in this instance is a secondarycheck valve in distinction from the described and appropriately termedmain check valve 114, with this secondary check valve 140 being in thisinstance mounted in the annular recess part 132 of the bypass 120, andnormally closed to block fluid flow from the port section 76 to the portsection 76. The instrumentality 138 provides in this instance a steppedcylinder aperture 142 with its larger and smaller ends open to thechamber parts 126 and 130, respectively, of the bypass 120, and astepped plunger 144 with larger and smaller ends 146 and 148 in thecylinder aperture 142, with the smaller plunger end 148 being providedwith a pin 150 in line and operatively associated with the secondarycheck valve 140. With this arrangement, and while hydraulic fluid underpressure is admitted to the chuck-closing cylinder side 26 and thehydraulic supply fluid remains substantially at its pressure, thepressure of the fluid in the chamber parts 126 and 130 of the bypass 120is the same, meaning that the total pressure of fluid on the largerplunger end 146 is greater than the total pressure of fluid on thesmaller plunger end 148, whereby the plunger is then held in the rightend position shown in which its pin 150 holds the secondary check valve140 open to thereby permit such of the trapped hydraulic fluid whichwould due to I operational heat-up increase the pressure of the latterappreciably beyond the prevailing normal pressure of the hydraulicsupply fluid, to reach the constriction 122 and bleed therethrough. Onthe other hand, if on a sudden pressure drop of the hydraulic supplyfluid its effect on the larger plunger end 146 is a sudden drop of thetotal fluid pressure on the latter anywhere below the total fluidpressure on the smaller plunger end 148, the plunger 144 will quickly bestepped to the left from the position shown and permit equally quickclosure of the secondary check valve 140 to thereby block any of thetrapped hydraulic fluid from reaching the constriction 122. A suddenpressure drop of the hydraulic supply fluid, while immediately effectiveon the larger plunger end 146, is not effectively transmitted to thehydraulic fluid in the chamber part 130 of the bypass 120 and, hence, tothe smaller plunger end 148, before the plunger 144 responds to the thengreater total fluid pressure on its smaller end 148 in stepping to theleft and thereby permitting quick closure of the secondary check valve140. This is due to the fact that on a sudden pressure drop of thehydraulic supply fluid the volumetric escape rate of hydraulic fluidfrom the chamber part 130 of the bypass 120 through the constriction 122is so very small that at the time the sudden pressure drop is effectiveon the larger plunger end 146, the pressure of the hydraulic fluid inthis chamber part 130 is sufficiently high forcefully to step theplunger 144 to the left from its shown valve-opening position. Of

course, the relative areas of the larger and smaller plunger ends 146and 148 are selected so that the plunger will, on a sudden pressure dropof the hydraulic supply fluid, be stepped from its valve-openingposition at a stage of the sudden pressure drop at which on closure ofthe secondary check valve the pressure of the hydraulic fluid ahead ofthe main check valve 1 14 and including that in the chuck-closingcylinder side 26 is sufficiently high to keep the work safely gripped inthe chuck. With this arrangement, a chuck operation, in the course ofwhich the pressure of the hydraulic supply fluid should suddenly drop,may in many instances be safely concluded before the increasingpressure, due to heat-up, of the hydraulic fluid in the chuck-closingcylinder side could reach hazardous proportions after the suddenpressure drop. However, for safe chuck operation in any event, there ispreferably also provided the beforementioned automatic control whichsenses the pressure of the hydraulic supply fluid and on a preset dropof the same acts to bring the power drive of the chuck to a stop atleast within a period from the preset pressure drop of the supply fluidduring which the increasing pressure of the hydraulic fluid in thechuck-closing cylinder side will safely remain below a hazardouspressure and many started chuck operations will be concluded.

While in the described chuck operating mechanism 10 the cylinder sides26 and 28 have been designated as the chuck-closing and chuck-openingcylinder sides, respectively, the exemplary mechanism may be used witheither cylinder side 26 or 28 being the chuckclosing side and the othercylinder side being the chuck-opening side since hydraulic fluid underpressure is admissible to either cylinder side and the other cylinderside simultaneously vented. In order to operate the present chuckoperating mechanism at the featured safety also when the cylinder side28 is the chuckclosing side and the other cylinder side 26 is thechuckopening cylinder side, there is interposed in the port 82 a secondmain check valve 114a which functions in exactly the same manner as theother main check valve 1 14, i.e., the second valve 114a closes and,hence, traps the hydraulic operating fluid in the chuck-closing cylinderside 128 when the pressure of the hydraulic supply fluid should suddenlydrop. The piston which is associated with the second main check valve114a is in this instance the same piston which is associated with theother main check valve 114, i.e., the piston 116 which, for itsassociation with valve 114a is provided with another pin 118a. Thus,when hydraulic fluid under pressure is admitted to the chuck-closingcylinder side 28 and the other cylinder side 26 is vented, hydraulicfluid under pressure in the port 82 will force the piston 116 into, andhold it in, a position to the left of that shown so that its pin 1180will permit closure of the second main check valve 114a.

For safe operation of the mechanisms 10 when the cylinder side 28 is thechuck-closing side, the mechanism further provides for bleeding from thechuckclosing cylinder side such of the hydraulic operating fluid thereinwhich, if not bled off, would progressively increase the pressure ofthis fluid due to operational heat-up of the latter as long as thepressure of the hydraulic supply fluid remains at its normal pressure,and also provides for blocking bleed-off of hydraulic fluid from thechuck-closing cylinder side 28 when the pressure of the hydraulic supplyfluid should suddenly drop. To these ends, the mechanism 10 provides thesame elements which are provided and described for safe operation inthese respects of the mechanism 10 when the cylinder side 26 is thechuck-closing cylinder side, with the major elements associated with thecylinder side 28 being denoted by the same reference numerals as theircounter elements associated with the cylinder side 26, except that thesuffix a is added to them. Safe operation in these respects of themechanism 10 is believed to be readily understood and requires nofurther description, in view of the described safe operation in the samerespects of the mechanism 10 when the cylinder side 26 is thechuck-closing side.

The casing 70, in which all the elements for safe chuck operation areprovided in this instance, is prefer ably made in suitably joinedsections 154, 156 and 158 for ready machining of the individual sectionsand ready assembly therewith of the additional elements before joiningthese sections.

In the exemplary chuck-operating mechanism 10 the elements making forthe described safe chuck operation are provided in a stationary part ofthe mechanism which in this instance is the casing 70 that is separateand apart from the stationary coupling part as described, but couldobviously also be formed as part of the stationary coupling part 20.This mechanism 10 is entirely satisfactory for safe chuck operation aslong as there is no leakage of hydraulic fluid between either main checkvalve and the associated chuck-closing cylinder side. Such leakage isindeed quite remote, except leakage at the fluid seals in the swivelcoupling that may be difficult to avoid, or cannot be avoided at all,with particular fluid seals, including fluid seals of larger sizes whichare subject to more severe heat-up from operational friction. Thus, ifsuch a leak, at the fluid seals should develop in the describedmechanism 10, safe chuck operation would be impossible because on asudden pressure drop of the hydraulic supply liquid, the main checkvalve and also the associated secondary check valve would immediatelyclose and thus trap the fluid between these check valves and thechuck-closing cylinder side, and any leak, even the slightest one, ofthis trapped fluid would quickly reduce the pressure of the latter belowa safe work-gripping level, for it takes comparatively little leakage ofthis non-compressible hydraulic fluid to do just that. Accordingly, inorder to render chuck operation safe where a leak in the hydraulic fluidline to the chuck-operating cylinder may occur, and is certain to occurwhere the fluid seals in the swivel coupling permit leakage, and eventhe slightest leakage, of hydraulic fluid, it is clearly indicated tolocate the elements for safe chuck operation as closely as possible tothe chuck-closing cylinder side, and in particular in the operationallyturning part of the swivel coupling between the fluid seals in thiscoupling and the chuck-closing cylinder side.

Reference is now had to FIG. 2, which shows modified chuck operatingmechanism in which the elements for safe chuck operation are located inthe operationally turning part 162 of the swivel coupling 164 betweenthe chuck-closing cylinder side and the fluid seals 166 in thiscoupling. The swivel coupling 164 is in this instance provided with acenter aperture 168 to clear work that may extend rearwardly from theassociated chuck in which the work is gripped for machining, with thestructure of the coupling being built around this center aperture and,hence, being of considerable diametr-ic dimensions which requires thefluid seals 166 to be of considerable diameters that may readily giverise to fluid leakage thereat in operation of the mechanism. The turningcoupling part 162 is mounted on the power Spindle of a lathe or the likewhich also carries the associated chuck for operational drive of both,the

chuck and turning coupling part.

The swivel coupling 164 has also a stationary part 170 which throughantifriction bearings 172 and 174 is mounted on a hollow axial shank of,and in this instance oii a separate sleeve 176 on, the turning couplingpart 162. The turning coupling part 162 provides a cylinder 178 with apiston 180 defining therein chuck-closing and chuck-opening cylindersides 182 and 184, respectively, with the piston 180 having in thisinstance'a hollow shank 186 slidable on the sleeve 176 on the turningcoupling part 162 and in a cylindrical opening 188 in.the latter, withthis shank 186 thus also forming part of the chuck-closing cylinder side182. The hollow shank 186 of the piston 180 is at 190 connected with ahollow draw bar 192 for operating the jaw" actuator of an associatedchuck.

The stationary coupling part 170 is provided with an opening 194 whichthrough a port 196 is in communication with the chuck-closing cylinderside 182, with this port-196 providing an orifice 198 leading from theopening 194 into and through a liner 200 in the coupling part 170 to aperipheral groove 202 in the sleeve 176 on the turning coupling part162, a continuing orifice 204 in the sleeve 176, and a continuingorifice 206 in the-turning coupling part that leads to the chuckclosingcylinder side 182 and is formed with an annular recess 208.

The stationary coupling part 170 is also provided with another opening210 which through a port 212 is in communication with the chuck-openingcylinder side 184,-with this port providing an orifice 214 leading fromthe opening 210 into and through the linear 200 in the coupling part 170to a peripheral groove 216 in the sleeve 176 on the turning couplingpart 162, the peripheral groove 216 and a continuing orifice 218 in thesleeve 176, and a continuing orifice 220 in the turning coupling part162 that leads to the chuck-opening cylinder side 184 and is formed withan annular recess 222.

Interposed in the port 196 within the turning coupling part 162, andmounted in the recess part 208 of this port 196, is a main check valve224 which is associated with the chuck-closing cylinder side 182, and isnormally closed to block fluid flow from the latter.

The openings 194 and 210 in the stationary coupling part 170 are throughconduits 226 and 228 connected with a control valve (not shown) which isoperative to admit hydraulic fluid under pressure from a suitable sourceto either opening 194 or 210 and simultaneously vent the other opening.In operation of the mechanism 160, and assuming that an associated chuckis to grip work for subsequently machining the latter in thepower-driven chuck, the mentioned control valve is operated to admithydraulic fluid under pressure from the source to the opening 194 in thestationary coupling part 170, and simultaneously vent the other opening210 and, hence, the chuck-opening cylinder side 184. Hydraulic fluidunder pressure thus admitted to the opening 194 in the coupling 164 willimmediately pass through the port 196 to the chuck-closing cylinder side182 and shift the piston 180 to the position shown in which the workwill be gripped by the chuck, with the hydraulic fluid in the port 196opening the main check valve 224 until the pressure of the fluid in thechuckclosing cylinder side 182 is substantially equal to that of thehydraulic supply fluid. The main check valve 224 will act, i.e., close,when there should be a sudden drop in pressure of the hydraulic supplyfluid, unless this check valve is then closed, thereby trapping thehydraulic operating fluid in the chuck-closing cylinder side, as nowreadily understood.

In order to release the gripped work from the chuck, the mentionedcontrol valve is operated to admit hydraulic fluid under pressure fromthe source or supply to the opening 210 in the coupling 164 and, hence,to the chuck-opening cylinder side 184, and simultaneously vent theother opening 194. However, with the main check valve 224 thenimmediately closing, if not then closed, and the hydraulic fluid in thechuckclosing cylinder side 182 being thus trapped therein, the piston180 will not respond to the hydraulic fluid in the chuck-openingcylinder side 184 until the other cylinder side 182 is vented. To thelatter end, there is slidable in an annular recess 228 in the turningcoupling part 162 a secondary piston 230 with a pin 232, with one end ofthis piston 230 being exposed to hydraulic fluid in the port 196, andits other end being exposed to hydraulic fluid in the other port 212through a branch thereof including an annular groove 234 in the turningcoupling part 162 and a continuing orifice 236 leading also to thechuck-opening cylinder side 184. Thus, with the opening 194 inthecoupling vented and hydraulic fluid under pressure admitted to the otheropening 210, for work release from the chuck, the secondary piston 222will, by the pressure of hydraulic fluid in the'port 212, be shifted toa position to the left of that shown and thereby open with its pin 232the check valve 224 to permit venting of the chuck-closing cylinder side182 and, hence, actuation of the main pistonl80 for work-release fromthe chuck.

The chuck operating mechanism also has a pressure control device 240which provides in the port 196 within the turning coupling part 162 abypass 242 around the check valve 244, on a constriction 244 in thisbypass. The bypass 242 is in this instance formed by an orifice 246which leads from the port 196 between the check valve 224 and thechuck-closing cylinder side 182, an annular recess 248, a chamber orreservoir 250, the constriction 244, and orifices 252 and 254, of whichorifice 254 leads to the port 196 between its crossing at the couplingparts and the check valve 224. The pressure control device 240 furtherprovides a fluid-responsive instrumentality 256, and a valve 258 whichis interposed in the bypass 242. The valve 258 is in this instance asecondary check valve which is mounted in the recess part 248 of thebypass 242, and is normally closed to block fluid flow from thechuckclosing cylinder side 182. The instrumentality 256 provides in thisinstance a stepped plunger 260 in a cylinder opening 262 in the turningcoupling part 162, with the plunger 260 carrying a pin 264 associatedwith the secondary check valve 258, and the larger and smaller ends 266and 268 of this plunger being exposed to the orifice and reservoir parts254 and 250, respectively, of the bypass 242.

It has already been mentioned that in this exemplary chuck operatingmechanism 160 hydraulic operating fluid may well leak past the sealingrings 166 in the coupling 164 in operation of the mechanism. To avoidmessy spillage of any leaking hydraulic fluid on the floor, thestationary coupling part 170 is provided at the opposite ends of theliner 200, and hence beyond the opposite ends of the grouped sealingrings 166, with annular escape passages 270 and 272 which at 274 and 276are open to a sump 278 in the bottom of the stationary coupling part170, with the sump 278 being by a conduit 280 connected with a tank (notshown) that holds a supply of hydraulic fluid from which fluid is drawnby a pump the output of which constitutes in this instance the source ofhydraulic fluid under pressure. The liner 200 is in this instanceprovided with a further escape passage 282 that leads to the sump 278.

In operation of the mechanism 160, and assuming that hydraulic fluidunder operating pressure is admitted to the opening 194 in the coupling164, and hence also to the chuck-closing cylinder side 182 through themain check valve 224, the check valve 224 will close when the pressureof the hydraulic fluid in the chuckclosing cylinder-side 182 isapproximately equal to the pressure of the hydraulic supply fluid. Onoperational heat-up, and ensuing increase in pressure, of the trapped.hydraulic fluid in the chuck-closing cylinder side due to operationalfriction in the coupling 164 and particularly at the sealing rings 166,the main check valve 224 will remain closed, but the secondary checkvalve 258 is then held open by the stepped plunger 260 to permitbleeding through the constriction 244 in the bypass 242 of sufficienthydraulic fluid from the chuckclosing cylinder side .182 to maintain thepressure of the fluid in the latter at an entirely safe level for theduration, no matter how long, of any chuck operation. However, in therare event of a sudden pressure drop of the hydraulic supply fluid, dueto pump failure or a sudden leak in the supply line to the main checkvalve 224, for example,'the stepped plunger 260 will quickly retract andpermit equally quick closure of the secondary check valve 258 also, totrap the hydraulic fluid under operating pressure in the chuck-closingcylinder side 182. The pressure of the hydraulic fluid thus trapped inthe chuck-closing cylinder side will, due to further heat-up, increaseto a level which is still entirely safe for the remaining duration ofmany started chuck operations, and certainly until a previouslymentioned automatic control responding to a sudden pressure drop of thehydraulic supply fluid acts to bring the power drive of the turningcoupling part 162 and associated chuck to a safe stop.

The present chuck operating mechanism thus affords entirely safe chuckoperation even if hydraulic fluid should, in normal operation of themechanism, leak from the supply line into the sump 278 in the stationarycoupling part 170, for in that case the constantly available hydraulicsupply fluid under pressure will, despite such leakage, keep thepressure in the supply line up to the main chuck valve 224 at fulloperating pressure. On the other hand, if the pressure of the supplyfluid in the turning coupling part 162 should drop suddenly from anycause whatever, such as pump failure or a sudden leak in the supplyline, the pressure control device 240 will act to keep the pressure ofthe hydraulic fluid in the chuck-closing cylinder side 182 at a safelevel either for the remaining duration of a started chuck operation,but certainly until after such a sudden pressure drop of the hydraulicsupply fluid the power drive of the turning coupling part 162 andassociated chuck has automatically been brought to a safe stop.

While in the description so far of the chuck operating mechanism 160 thecylinder side 182 has been referred to as the chuck-closing cylinderside, the mechanism is readily suited for safe chuck operation witheither cylinder side 182 or 184 being the chuck-closing cylinder sideand the other cylinder side being the chuckopening cylinder side. To thelatter end, there is interposed in the port 212 in the turning couplingpart 162 another main check valve 224a which is associated with thecylinder side 184, and there is further provided in the turning couplingpart another secondary piston 230a associated with the main check valve224a and operative to open the latter for operational venting of thecylinder side 184. Still to the same end, the chuck operating mechanism160 provides another pressure control device 240a which in its structureand operation is quite similar to the described pressure control device240 and, hence, requires no further description, with prominent elementsof the pressure control device 240a being in FIG. 2 denoted by the samereference numerals as their counter elements of the pressure controldevice 240, except that the suffix a has been added to them.

While in FIG. 2 the pressure control devices 240 and 240a are, forsimplicity of illustration, shown spaced radially outwardly from therespective associated main check valves 224 and 224a, it is entirelyfeasible, and much preferred, to arrange the pressure control devices240 and 240a on one side or the other of the respective main checkvalves 224 and 224a, for example, to thereby keep the turning couplingpart 162 at a considerably smaller outer diameter.

Reference is now had to FIG. 3 which shows diagrammatically a furthermodified pressure control device 290. Thus, the reference numeral 292denotes a port through which to admit hydraulic fluid under supplypressure to the chuck-closing cylinder side of the mechanism, with thehydraulic fluid passing in the direction of the arrow 294. Interposed inthe port 292 is a main check valve 296 which is normally closed to blockfluid flow from the chuck-closing cylinder side. Provided in the port292 is a bypass 298 around the main check valve 296, and interposed inthis bypass 298 is a secondary valve 300 which, when open as shown,forms part of the bypass 298. In this form of the pressure controldevice 290, the constriction in the bypass is formed by a constrictedpassage 302 in the secondary valve 300, and the fluid-responsiveinstrumentality is in the form of a flexible diaphragm 304 in a chamber306, with the diaphragm 304 dividing the chamber 306 into sections 308and 310. The chamber section 308 is, through a conduit 312 and acontinuing part of the bypass 298 on one side of the secondary valve300, in communication with the section 292a of the port 292 between thehydraulic fluid pressure source and the main check valve 296, and theother chamber section 310 is, through a conduit 314 and a continuingpart of the bypass 298 on the other side of the secondary valve 300, incommunication with the section 292k of the port 292 between the checkvalve 296 and the chuck-closing cylinder side. In operation of thepressure control device 290, and assuming that hydraulic fluid under thesupply pressure has just been admitted to the chuck-closing cylinderside through the port 292 and interposed main check valve 296, thelatter will close when substantial pressure equilibrium prevails in bothport sections 292a and 292b, with the secondary valve 300 being thenopen, i.e., its constricted passage 302 forming part of the bypass 298.On operational heat-up of the hydraulic fluid in the chuckclosingcylinder side in the course of a chuck operation, and with the maincheck valve 296 then remaining closed, the ensuing increase in pressureof this hydraulic fluid is also effective in the chamber part 310 on oneside of the diaphragm 304, and any responsive flexure of this diaphragm,such as the exemplary flexure shown, will keep the secondary valve 300with its constricted passage 302 in communication with the bypass 298 topermit bleeding therethrough of such of the hydraulic fluid in thechuck-closing cylinder side which, if not bled off, would cause furtherincrease in pressure of the hydraulic fluid in the chuck-closingcylinder side. However, in the rare event of a sudden pressure drop ofthe hydraulic supply fluid in the line up to the main check valve 296,this sudden pressure drop is immediately effective in the chambersection 308, and the diaphragm 304 will immediately respond to thehydraulic fluid under the higher pressure in the other chamber section310 in flexing sufficiently to retract the secondary valve 300 into aclosed position in which its constricted passage 302 is out ofcommunication with the bypass 298 and, hence, permits no longer bleedingof any hudraulic fluid from the chuck-closing cylinder side.

Reference is finally had to FIG. 4 which shows diagrammatically a stillfurther modified pressure contlol device 290' which may in all respectsbe like the pressure control device 290 of FIG. 3, except that theconstriction 302 is provided, not in the secondary valve 300', butdirectly in the bypass 298 on either or both sides of the secondaryvalve 300', and the secondary valve 300' is provided in this instancewith a peripheral groove 320 which in normal chuck operation is incommunication with the bypass 298' to permit bleeding of excesshydraulic fluid from the chuck-closing cylinder side through theconstriction 302, with the secondary valve 300 being, on a suddenpressure drop of the supply fluid, shifted by responding flexure of thediaphragm 304' into a closed position in which its peripheral groove 320is out of communication with the bypass 298' and more particularly withits constriction 302'. The present pressure control device is furthermodified in that in non-flexed condition of the diaphragm 304', i.e.,when there is substantial fluid pressure equilibrium in the fluid linesections ahead of and behind the main check valve, the secondary valve300' is also closed, as shown. However, once hydraulic fluid under thesupply pressure is admitted to the chuckclosing cylinder side and themain check valve is closed, the pressure of the hydraulic fluid in thechuck closing cylinder side will, due to operational heat-up of thisfluid in chuck-operation, increase, and it is only on such increase ofthe pressure of this fluid that the diaphragm 304 will respond to shiftthe secondary valve 300 to open position in which its peripheral groove320 is just in communication with the constriction 302' in the bypass298' to permit bleeding therethrough of excess hydraulic fluid from thechuck-closing cylinder side.

What is claimed is:

1. In hydraulic chuck operating mechanism, the combination of a swivelcoupling with stationary and operationally turning companion parts, ofwhich the turning part provides a cylinder with a piston definingtherein a chuck-closing cylinder side; a conduit, including a port insaid coupling leading to said cylinder side, for passing hydraulic fluidunder pressure to said cylinder side, with said port crossing saidcoupling parts; port sealing means in said coupling at the portcrossing; a check valve in said conduit dividing the same into first andsecond conduit sections of which said second section extends from saidvalve to said cylinder side, with said valve being normally closed toblock fluid flow from said cylinder side, and being opened by fluid insaid first conduit section under a pressure in excess of that of fluidin said cylinder side to introduce fluid into said cylinder side andopened by piston means to release fluid from said cylinder side; and afluid pressure control for said cylinder side, providing a bypass insaid conduit around said check valve, a second valve in said bypassforming part of the latter when open, a constriction in said bypass, andfluid pressure responsive means operatively associated with said secondvalve and having opposite faces exposed to fluid in said bypass onopposite sides, respectively, of said constriction to open and closesaid second valve when the pressure of hydraulic fluid in said secondconduit section is within a certain range and is above said range,respectively, with said range being from a pressure at least equal to,to a pressure of predetermined excess over, the pressure of hydraulicfluid in said first conduit section.

2. The combination in hydraulic chuck operating mechanism as in claim 1,in which said second valve is a secondary check valve in said bypassbetween said constriction and second conduit section and being normallyspring-closed to block fluid flow from said cylinder side, and saidfluid pressure responsive means is a slidable stepped plunger withlarger and smaller ends exposed to hydraulic fluid in said bypassbetween said first conduit section and constriction and between saidconstriction and second check valve, respectively, with said plungerbeing moved into advance and retract positions when the total pressureof fluid on said larger plunger end is greater and smaller,respectively, than the total pressure of fluid on said smaller plungerend, and said plunger in its advance and retract positions opening saidsecondary check valve and permitting its closure, respectively.

3. The combination in hydraulic chuck operating mechanism as in claim 2,in which there is further provided a reservoir in said bypass betweensaid constriction and said secondary check valve, and said smallerplunger end is exposed to and forms part of said reservoir.

4. ln hydraulic chuck operating mechanism, the combination of a swivelcoupling with stationary and operationally turning companion parts, ofwhich the turning part provides a cylinder with a piston definingtherein first and second cylinder sides; first and second conduits,including first and second ports, respectively, in said coupling, withsaid first and second ports leading to said first and second cylindersides, respectively, and crossing said coupling parts, and said conduitsbeing adapted for connection with a valve to admit hydraulic fluid underpressure to either conduit and simultaneously vent the other conduit;port sealing means in said coupling at the port crossings; a first checkvalve in said first conduit normally closed to block fluid flow fromsaid first cylinder side, and dividing said first conduit into first andsecond conduit sections of which said second section extends from saidcheck 'valve to said first cylinder side, with said first check valvebeing opened by fluid in said first conduit section under a pressure inexcess of that of fluid in said second conduit section; a secondslidable piston with opposite ends exposed to hydraulic fluid in saidfirst conduit section and in said second conduit, respectively, withsaid second piston being by hydrauic fluid under pressure in said firstconduit section and in said second conduit moved into first and secondpositions, respectively, in which to permit closure of said check valveand to open the same, respectively; and a fluid pressure control forsaid first cylinder side, providing a bypass in said first conduitaround said check valve, a second valve in said bypass forming part ofthe latter when open, a constriction in said bypass, and fluid pressureresponsive means operatively associated with said second valve andhaving opposite faces exposed to fluid in said bypass on opposite sides,respectively, of said constriction to open and close said second valvewhen the pressure of hydraulic fluid in said second conduit section iswithin a certain range and is above said range, respectively, with saidrange being from a pressure at least equal to, to a pressure ofpredetermined excess over, the pressure of hydraulic fluid in said firstconduit section.

5. The combination in hydraulic chuck operating mechanism as in claim 4,in which there is further provided a second check valve in said secondconduit normally closed to block fluid flow from said second cylinderside and dividing said second conduit into third and fourth conduitsections of which said fourth section extends from said second checkvalve to said second cylinder side, with said second check valve beingopened by fluid in said third conduit section under a pressure in excessof that of fluid in said fourth conduit section, and a third slidablepiston with opposite ends exposed to hydraulic fluid in said firstconduit and in said third conduit section, respectively, with said thirdpiston being by hydraulic fluid under pressure in said third site facesexposed to fluid in said second bypass on opposite sides, respectively,of said second constriction to open and close said third valve when thepressure of hydraulic fluid in said fourth conduit section is within acertain range and is above said range, respectively, with said rangebeing from a pressure at least equal to, to a pressure of apredetermined excess over, the pressure of hydraulic fluid in said thirdconduit section.

1. In hydraulic chuck operating mechanism, the combination of a swivelcoupling with stationary and operationally turning companion parts, ofwhich the turning part provides a cylinder with a piston definingtherein a chuck-closing cylinder side; a conduit, including a port insaid coupling leading to said cylinder side, for passing hydraulic fluidunder pressure to said cylinder side, with said port crossing saidcoupling parts; port sealing means in said coupling at the portcrossing; a check valve in said conduit dividing the same into first andsecond conduit sections of which said second section extends from saidvalve to said cylinder side, with said valve being normally closed toblock fluid flow from said cylinder side, and being opened by fluid insaid first conduit section under a pressure in excess of that of fluidin said cylinder side to introduce fluid into said cylinder side andopened by piston means to release fluid from said cylinder side; and afluid pressure control for said cylinder side, providing a bypass insaid conduit around said check valve, a second valve in said bypassforming part of the latter when open, a constriction in said bypass, andfluid pressure responsive means operatively associated with said secondvalve and having opposite faces exposed to fluid in said bypass onopposite sides, respectively, of said constriction to open and closesaid second valve when the pressure of hydraulic fluid in said secondconduit section is within a certain range and is above said range,respectively, with said range being from a pressure at least equal to,to a pressure of predetermined excess over, the pressure of hydraulicfluid in said first conduit section.
 2. The combination in hydraulicchuck operating mechanism as in claim 1, in which said second valve is asecondary check valve in said bypass between said constriction andsecond conduit section and being normally spring-closed to block fluidflow from said cylinder side, and said fluid pressure responsive meansis a slidable stepped plunger with larger and smaller ends exposed tohydraulic fluid in said bypass between said first conduit section andconstriction and between said constriction and second check valve,respectively, with said plunger being moved into advance and retractpositions when the total pressure of fluid on said larger plunger end isgreater and smaller, respectively, than the total pressure of fluid onsaid smaller plunger end, and said plunger in its advance and retractpositions opening said secondary check valve and permitting its closure,respectively.
 3. The combination in hydraulic chuck operating mechanismas in claim 2, in which there is further provided a reservoir in saidbypass between said constriction and said secondary check valve, andsaid smaller plunger end is exposed to and forms part of said reservoir.4. In hydraulic chuck operating mechanism, the combination of a swivelcoupling with stationary and operationally turning companion parts, ofwhich the turning part provides a cylinder with a piston definingtherein first and second cylinder sides; first and second conduits,including first and second ports, respectively, in said coupling, withsaid first and second ports leading to said first and second cylindersides, respectively, and crossing said coupling parts, and said conduitsbeing adapted for connection with a valve to admit hydraulic fluid underpressure to either conduit and simultaneously vent the other conduit;port sealing means in said coupling at the port crossings; a first checkvalve in said first conduiT normally closed to block fluid flow fromsaid first cylinder side, and dividing said first conduit into first andsecond conduit sections of which said second section extends from saidcheck valve to said first cylinder side, with said first check valvebeing opened by fluid in said first conduit section under a pressure inexcess of that of fluid in said second conduit section; a secondslidable piston with opposite ends exposed to hydraulic fluid in saidfirst conduit section and in said second conduit, respectively, withsaid second piston being by hydrauic fluid under pressure in said firstconduit section and in said second conduit moved into first and secondpositions, respectively, in which to permit closure of said check valveand to open the same, respectively; and a fluid pressure control forsaid first cylinder side, providing a bypass in said first conduitaround said check valve, a second valve in said bypass forming part ofthe latter when open, a constriction in said bypass, and fluid pressureresponsive means operatively associated with said second valve andhaving opposite faces exposed to fluid in said bypass on opposite sides,respectively, of said constriction to open and close said second valvewhen the pressure of hydraulic fluid in said second conduit section iswithin a certain range and is above said range, respectively, with saidrange being from a pressure at least equal to, to a pressure ofpredetermined excess over, the pressure of hydraulic fluid in said firstconduit section.
 5. The combination in hydraulic chuck operatingmechanism as in claim 4, in which there is further provided a secondcheck valve in said second conduit normally closed to block fluid flowfrom said second cylinder side and dividing said second conduit intothird and fourth conduit sections of which said fourth section extendsfrom said second check valve to said second cylinder side, with saidsecond check valve being opened by fluid in said third conduit sectionunder a pressure in excess of that of fluid in said fourth conduitsection, and a third slidable piston with opposite ends exposed tohydraulic fluid in said first conduit and in said third conduit section,respectively, with said third piston being by hydraulic fluid underpressure in said third conduit section and in said first conduit movedinto first and second positions, respectively, in which to permitclosure of said second check valve and to open the same, respectively;and another fluid pressure control for said second cylinder side,providing a second bypass in said second conduit around said secondcheck valve, a third valve in said second bypass forming part of thelatter when open, a second constriction in said second bypass, and fluidpressure responsive means operatively associated with said third valveand having opposite faces exposed to fluid in said second bypass onopposite sides, respectively, of said second constriction to open andclose said third valve when the pressure of hydraulic fluid in saidfourth conduit section is within a certain range and is above saidrange, respectively, with said range being from a pressure at leastequal to, to a pressure of a predetermined excess over, the pressure ofhydraulic fluid in said third conduit section.